A series of polycyclic coumarins were isolated, through the natural products screening program at the National Cancer Institute, from several tropical plants of the genus Calophyllum in Sarawak, Malaysia. These natural products, including (+)-calanolide A (1, NSC 650886),.sup.1-4 (-)-calanolide B (costatolide) (2, NSC 661122),.sup.1,5 and soulattrolide (3),.sup.6 were identified as HIV-1- specific nonnucleoside reverse transcriptase inhibitors (NNRTIs).sup.1,2,7-9 with unique drug-resistance profiles..sup.10-13 (+)-Calanolide A (1), the most potent compound in the series, was selected for further development and is currently in clinical trials to evaluate its safety and pharmacokinetics of single and multiple doses in normal healthy volunteers..sup.18 After oral administration, (+)-calanolide A (1) was generally well tolerated and no patterns indicative of a safety concern were observed. .sup.18 Plasma concentrations of (+)-calanolide A (1) in humans were higher than anticipated from animal data and it appeared that therapeutic levels can be achieved in humans..sup.18. Because of our ongoing interest in developing (+)-calanolide A (1) and related compounds, we were interested in developing other (+)-calanolide, A analogues, such as costatolide (2) as a possible alternative to calanolide A(1). ##STR1##
Unlike (+)-calanolide A (1), which is extremely limited from natural sources, with the best yields obtained thus far being approximately 1 mg/g extract,.sup.6 costatolide (2) is rich in the latex of Calophyllum teysmannii, a very abundant plant species..sup.6 A yield of 48% costatolide (2) was isolated from the latex extractables by repetitive chromatographies including preparative HPLC..sup.6 Since latex harvests could, in theory, be sustained over an extended period of time and would not be destructive to the plant, sufficient supplies of costatolide (2) could be obtained from natural sources for preclinical and clinical development, and possible commercialization,.sup.14 providing that a scalable isolation method could be developed which is superior to the synthetic approaches.sup.2, 15 and earlier isolation approaches.sup.6,19 in terms of overall yield, cost effectiveness, and environmental implications. For instance, U.S. Pat. No. 5,591,770 describes the isolation of costatolide and soulattrolide in small quantities by HPLC, a tedious and high cost method which is not suitable for industrial production of costatolide and soulattrolide.